Referências Bibliográficas

http://books.google.com.br/books?hl=pt-BR&lr=&id=Kj7YPbL-LAYC&oi=fnd&pg=PA21&dq=significado+do+n%C3%BAmero+tres&ots=PJjhxI3EQZ&sig=lWyKY4HfEf8mAJjiPSfRt6MObL0#v=onepage&q&f=false